We propose to continue behavioral and anatomical analysis of the chemotaxis-, thermotaxis-, and developmentally-defective mutants of the nematode Caenorhabditis elegans which we have isolated in previous years. Our primary goal is to correlate the behavioral deficits of these mutants with the anatomical defects in their sensory nervous systems. We also propose to isolate additional mutants, defective in responses to repellents, which should provide a new class of chemotaxis-defective mutants for similar study. Finally, we propose to continue work with laser microbeams, in order to produce localized lesions in the sensory nervous system and to determine their behavioral consequences.